Polishing pads



E. W. MAASS POLISHING PADS Feb. 1, 1955 2 Sheets-Sheet 1 Filed Feb. 2,1949 s m MA VM w a A w D e ATTORNEY E. W. MAASS POLISHING PADS Feb. 1,1955 2 Sheets-Sheet 2 Filed Feb. 2, 1949 INVENTOR.

EDWARD W. MAASS ATTORNEY United States Patent POLISHING PADS Edward W.Maass, South Woodstock, Conm, assignor to American Optical Company,Southbridge, Mass., :1 voluntary association of MassachusettsApplication February 2, 1949, Serial No. 74,180

11 Claims. (Cl. 51-298) This invention relates to improved means andmethods of forming polishing pads and has particular reference toforming polishing pads of a type used in the ophthalmic art forpolishing the surfaces of glass articles such as ophthalmic lenses.

One of the principal objects of the invention is to provide a relativelydense solid polishing pad that is inherently abrasive-free and composedessentially of cellulosic particles of corn cob or wood flours held inadjacent bonded relation with each other by a matrix of bonding materialand formed to have an effective surface of a controlled fhape for use inpolishing the surfaces of articles such as enses.

Another object is to provide a polishing pad of the above character andmethod of making the same which embodies particles of ligno-cellulosematerial such as corn cob or wood flours held in bonded relation witheach other by a matrix of a vulcanizable elastomeric material and havinga controlled surface shape, which matrix can be formed by conventionalmethods to produce a pad of a substantially uniform thickness suitablefor use with conventional polishing machines.

Another object is to provide polishing means of the above character andmethod of making the same which embodies finely divided particles ofcorn cob wood flours substantially uniformly dispersed throughout amatrix or binder possessing an inherently elastomeric character which isresistant to oxidation and which is of such nature that the surface maybe wetted by the slurry of polishing compounds such as rouge and water,clay and water, or any of the other commonly known polishing compounds.

Another object is to provide a polishing pad of the above characterprovided with recessed and raised areas on its effective surface wherebysaid raised areas will be free to flex and more uniformly allow the padto conform to the shape of the surface of the article or articles beingpolished and said recessed areas will tend to retain therein the slurryor polishing compound thus insuring a more uniform distribution of saidcompound during the polishing operation.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings, in which:

Fig. 1 is a diagrammatic front elevational view illustrating anembodiment of the invention;

Fig. 2 is a plan view of a polishing pad embodying the invention;

Fig. 3 is a sectional view illustrating a modification in the polishingpad and method of using same;

Fig. 4 is a fragmentary plan view of the polishing surface of themodified pad;

Fig. 5 is a fragmentary sectional view of the pad diagrammaticallyillustrating its yielding characteristics during a polishing operation;

Fig. 6 is a fragmentary plan view of a pad having-different surfaceirregularities; and

Fig. 7 is a sectional view taken on line 77 of Fig. 6.

Referring more particularly to the drawings wherein like characters ofreference designate like parts throughout the views, the invention isdirected particularly to the provision of a polishing pad 3 embodyingfinely divided particles of ligno-cellulose material such as corn cob orwood flours substantially uniformly dispersed throughout a suitablematrix or binder and shaped to have a surface conforming substantiallyto that of the shape of the surface of an article 4 to be polished bysaid pad. The surice embodying the invention, is preferably shapedsubstantially to the final shape desired by fine grinding with emery orthe like after first being formed by commonly known rough grindingmethods employed in the ophthalmic art as through the use of coarseabrasives, diamond abrading tools or other suitable means.

In the drawing there is diagrammatically illustrated one method ofpolishing an ophthalmic lens 4 or other similar article. Referring toFig. l, the pad 3 is shown secured to a support 5 by a layer or coatingof adhesive 6 such as rubber cement, pitch, or other conventional andWell known adhesives. The support 5 is carried by a spindle 7 rotatablymounted within a bearing 8 and driven by any suitable source of powerthrough means such as pulley 9 and belt 10. The lens blank or otherarticle 4 to be polished is secured to a block 11 by means such as alayer of pitch 12 or other suitable adhesive commonly used in the art.The block 11 is provided with a socket 113 in which is extended a pinmember 14 carried by a supporting member 15, which member is carried bya shaft 16 rotatably mounted in a suitable bearing 17. The shaft 16 maybe rotated by any suitable means such as a pulley 18 and belt 19, whichmeans may be operated by any suitable source of power.

The polishing operation is performed by applying to the exposed surfaceof the pad 3 a suitable polishing compound such as rouge and water, clayand water, or any other of the well known glass polishing compounds, andby causing the pad 3 to be rotated through rotation of the shaft 7, andfinally causing the article 4 to be moved over the surface of the pad 3in a path controlled by the eccentric relationship of the pin 14 andshaft 16 which is in turn rotated.

It has been found that in the past some polishing compounds, althoughextremely efiective as glass polishing agents, have caused considerablewear of polishing pads particularly when such pads were made of felt asnow commonly used in the art. The pad 3 as described above has beenfound to be much more resistant to wear during the polishing operationand has a life which greatly exceeds that of the above mentionedcommonly used pad materials.

The pad 3 which embodies a plurality of finely divided particles 2'0 ofligno-cellulosic material substantially uniformly dispersed throughout abinder or matrix 21 can be fabricated in sheet form or to a controlledshape. One matrix or binder which has proven to be very effective iscompounded from rubber, either natural or synthetic; others fromplastics.

As an example, the following formula produces a desirable pad usingapproximately 205 parts by weight of natural rubber as "the majoringredient in the matrix:

To this formula is added approximately 200 parts by weight of particlesof ligno-cellulosic material such as corn cob or an amount ranging fromapproximately to 600 parts by weight, and preferably between 35 and 60mesh. It is essential that all of the ingredients be free from particlesof metal such as iron, or bits of sand or grit, that is, any materialwhich would be hard enough to cause scratching of the surface of thearticle being polished. V

A ligno-cellulose material of the fibrous-woody type, imparts improvedpolishing characteristics to the resultant pad and others such as walnutshell flour, mahogany and pine and wood fiours like might be used, withcorn cob particles, however, being preferable. Fillers such as clay,rouge, carbon black or other similar ingredients may be added to theligno-cellulose ingredient if desired, it being necessary, however, forsatisfactory results, to include the ligno-cellulose ingredient as atleast 50% of the filler.

The bonding material of said formula may comprise synthetic rubber suchas butadiene-acrylonitrile copolymer rubber, organic polysulfide rubber,polyisobutylene rubber, or reclaimed rubber, or colloidal blends ofbutadiene-acrylonitrile copolymer rubber and polyvinyl chlorides, theseingredients to be substituted for the natural rubber in Table A eitherin whole or in part or in combination and so embody about 200 to 205parts by weight of the mix. Reduction or increase in the abovequantities of vulcanizing agents may be necessary to secure comparablephysical properties when mixtures are made by substituting synthetic orreclaimed rubber in the above mentioned formula. The sulphur is howeverpreferably kept within the range of 4 to 12 parts by weight.

Plasticizers other than coumarone-indene resin may be used if desiredsuch as stearic acid, chlorinated diphenyls, dioctyl phthalate, anddiglycol sebacate and the like. They may be varied between and parts byweight.

Three other formulas producing satisfactory pads in accordance with thepresent invention are:

Table B Parts by Weight Butadieneacrylonitrile copoly'mer rubber Blendof Butadienaacrylonitrile copolymer rubber and polyvinyl chlorideSulphur Zinc Oxide Benzothiazyl Disulphide Zine Salt of Coconut OilFatty A (is Chlorinated Diphenyl gliglycol Sebacate Corn Cob Polysulfidetype Synthetic Rubber Polymer" Ooumarone-indene resin Tetrametbylthiuram monosulphide between the dies, pressing it to the shape desired,and

then subsequently applying heat while held under pressure.

Since there is produced a substantially uniform dispersion of cob in anyof the above matrix material the thickness of the polishing pad used isimmaterial provided that the surface in contact with the glass is shapedsubstantially to the surface shape of the article being polished.

Such a pad as disclosed herein can be easily adapted to simultaneouslypolish a plurality of articles such as ophthalmic lenses rather than asingle article. Such a polishing operation is diagrammaticallyillustrated in Fig. 3 wherein a plurality of lenses 22 are attached, asby a layer of pitch or other suitable adhesive 23, to a block 24 orsimilar lens holding device with the surfaces of the lenses to bepolished directed toward the polishing pad 25. The pad 25 is shapedsubstantially to the shapes of the surfaces of the lenses and is securedto a support 26 by a layer or coating of suitable adhesive 27, such asrubber cement, pitch or the like, the support 26 being mounted foroscillating or rotating movement so as to move the pad 25 over thesurfaces of the lenses 22.

The surfaces of the lenses 22, which are to be polished by the pad 25embodying the invention, will preferably be shaped substantially to thefinal shape desired by fine grinding with emery or the like after firstbeing formed by commonly known rough grinding methods.

The polishing operation is performed similarly to the method describedin connection with Fig. l by applying to the exposed surface of the pad25 a suitable polishing compound such as rouge and water, clay andwater, or any other of the well known glass polishing compounds, and bycausing the pad 25 to be moved over the surfaces of the lenses 22through conventional means, and finally causing the block 24 carryingthe lenses 22 to be rotated so that the cooperating movements of thesupport 26 and the block 24 will cause the pad 25' to polish thesurfaces of all the lenses 22.

It has been found that when blocks 24 are provided with lenses 22 whichhave'been previously surfaced and rough polished, the radii ofcurvatures of the partially finished lens surfaces may vary slightlyfrom one another and from the radius of curvature of the polishing paddue to various conditions such as wear or misalignment of machine partsused in any of the preceding lens surfacing operations or in attachingthe lenses to the block 24, so that it has been found that the radii ofall of the lens surfaces in some instances do not conform to the radiusof the pad, thus causing certain portions of the surfaces to beincompletely polished when rigid pads are used. In such instances thepolishing pads may polish only portions of the lenses while leavinguntouched the remaining portions of the lenses.

Although the pad possesses some inherent yielding characteristics due toits composition, it has been found desirable in instances where there isa variation in surface characteristics of the lenses to provideadditional means to insure complete conformation of the polishingsurface of the pad to the lens surfaces. This is done by providing thepad with an irregular polishing surface as illustrated in Figs. 3-7. Thepreferred method is to form alternate spaced concentric grooves andridges 20 and 29 respectively.

Thus, in cases where there is a variation in radii between a lenssurface and the surface of the pad, the application of the necessarypolishing pressure to the pad will cause displacement of the ridges 29so that these ridges will maintain substantial engagement with thesurface of the glass to be polished. This is illustrated in Fig. 5wherein a lens 22 which has the desired surface curvature conforming tothe radius of the pad surface is located on the block 24, and heldthereon by the adhesive 23. This lens 22 will be engaged by the ridges29 formed on the pad 25 substantially as shown by solid lines. However,when a lens 22 is poorly attached to the block or provided with asurface curvature having a radius different than the abrading surface ofthe pad, such as shown by dotted outline, the ridges 29 will be inclinedto substantially the positions indicated by dotted lines. This featureassures that all surfaces of the lenses 22, regardless of variationstherein, will be efiiciently polished.

It has also been found in the past that after considerable use polishingpads which are formed with a continuous substantially smooth or evensurface are apt to glaze, the glazed surfaces resulting in veryineficient polishing. By providing the pad 25 with the grooves 28 thepolishing surfaces of the ridges 29 are less apt to become glazed due tothe deformable characteristics thereof.

During polishing operations, it has also been found that at times theslurry or polishing compound which is initially applied to the effectivesurface of the pad may be thrown off to such an extent that anadditional amount must necessarily be added or the polishing done withlittle or no compound resulting in inefficient polishing. However, witha pad formed according to the present disclosure, the polishing compoundor slurry will gather in the grooves 28 and so will continuouslylubricate the surfaces of the lenses 22 being polished during thepolishing operation.

Although the preferable surface structure of a pad 25 is illustrated inFigs. 3, 4 and 5, it is to be understood that the polishing surface ofthe pad may be, if desired, formed with straight, parallel grooves 30(Figs. 6 and 7), thus leaving raised squares or flats 31 which will bein abutment with the articles being polished, or with grooves cutradially or tangentially and in parallel or staggered relation.

From the foregoing description it will be understood that byincorporating a controlled amount of corn cob or Wood flour particles ina natural or synthetic rubber matrix, a polishing pad can be fabricatedtherefrom on plasticizing and vulcanizing, which pad will have improvedefficiency and wear resistance characteristics, and by providing thepolishing pad with an irregular abradmg surface as described the padwill have still greater efiiciency and wear resistance characteristicsas well as ability to conform to the shapes of the surfaces beingpolished, and will accomplish all the objects of this mventlon.

Reference may be also had to the copending patent application of AlbertJ. Laliberte, Serial No. 74,066, filed of even date with this patent andowned by the same assignee wherein there are disclosed and claimed otherpolishing pads embodying mixtures of natural or synthetic rubbers withcontrolled amounts of thermoplastic resins and cellulosic fillers.

While the novel features of the invention have been shown and describedand are pointed out in the annexed claims, it will be understood thatvarious omissions, substitutions, and changes in and widely difierentembodiments of the invention can be made without departing from thescope thereof and it is intended that all matters contained in the abovedescription and shown in the accompanying drawings be interpreted asillustrative and not in a limiting sense.

I claim:

1. An inherently substantially abrasive-free pad for use in polishingglass articles, said pad comprising the vulcanized relatively densesolid product of approximate ly 205 parts by weight of rubber,approximately from 8-12 parts by weight of sulphur, approximately from5-7 parts by weight of zinc oxide, approximately from 3-5 parts byweight of zinc stearate, approximately from O.30.6 part by weight ofthiuram monosulfide, approximately from 4-6 parts by weight ofbenzothiazyl disulfide, approximately from 5-20 parts by weight ofcoumarone-indene resin, and approximately from 100-600 parts by weightof corn cob particles.

2. An inherently substantially abrasive-free pad for use in polishingglass articles, said pad comprising the vulcanized relatively dense,solid product of approximately 205 parts by weight of rubber,approximately parts by weight of sulphur, approximately 6 parts byweight of zinc oxide, approximately 4 parts by weight of zinc stearate,approximately 0.4 part by weight of thiuram monosulfide, approximately 5parts by weight of benzo thiazyl disulfide, approximately 10 parts byweight of coumarone-indene resin, and approximately 200 parts by weightof corn cob particles.

3. The method of making a pad for use in polishing glass articles havingcontrolled surface shapes comprising the steps of making a mixturecontaining approximately 205 parts by weight of rubber, approximatelyfrom 812 parts by weight of sulphur, approximately from 5-7 parts byweight of zinc oxide, approximately from 35 parts by weight of zincstearate, approximately from 0.30.6 part by weight of thiurammonosulfide, approximately from 4-6 parts by weight of benzothiazyldisulfide, approximately from 5-20 parts by weight of plasticizer,bonding together the particles of approximately from 100600 parts byweight of corn cob of sizes ranging approximately from 35 to 60 meshwith said mixture, and under heat and pressure vulcanizing said mixtureto form a relatively dense solid having a surface shaped substantiallyto the shape of the surface to be polished.

4. The method of making a pad for polishing glass articles havingcontrolled surface shapes comprising the steps of making a mixturecontaining approximately 205 parts by weight of rubber, approximately 10parts by weight of sulphur, approximately 6 parts by weight of zincoxide, approximately 4 parts by weight of zinc stearate, approximately0.4 part by weight of thiuram monosulfide, approximately 5 parts byweight of benzothiazyl disulfide, approximately 10 parts by weight ofplasticizer, adding to this mixture approximately 200 parts by weight,of corn cob particles of sizes ranging approximately from 35 to 60mesh, and then under heat and pressure vulcanizing the whole to arelatively dense solid having a surface shaped substantially to theshape of the surface to be polished.

5. An inherently substantially abrasive-free pad for use in polishingglass articles consisting of the vulcanized product of approximately 100parts by weight of butadiene-acrylonitrile copolymer rubber,approximately 100 parts by weight of a blend of butadiene-acrylonitrilecopolymer and polyvinyl chloride, approximately 4 parts by weight ofsulphur, approximately 6 parts by weight of zinc oxide, approximately 5parts by weight of benzothiazyl disulphide, approximately 4 parts byweight of zinc salt of coconut oil fatty acids, approximately 20 partsby weight of chlorinated diphenyl, approximately 20 parts by weight ofdiglycol sebacate, approximately 50 parts by weight of clay, andapproximately 250 parts .6 by weight of corn cob particles, saidvulcanized product being a relatively dense "solid mass shaped to beuseful for polishing said glass articles.

6. An inherently substantially abrasive-free pad for use in polishingglass articles consisting of the vulcanized product of approximately 75parts by weight of butadiene-acrylonitrile copolymer rubber,approximately 70 parts by weight of a blend of butadiene-acrylonitrilecopolymer and polyvinyl chloride, approximately 10 parts by weight ofsulphur, approximately 6 parts by weight of zinc oxide, approximately 5parts by weight of benzothiazyl disulphide, approximately 4 parts byweight of zinc salt of coconut oil fatty acids, approximately 200 partsby weight of corn cob particles, approximately 60 parts by weight ofpolysulfide type synthetic rubber polymer, approximately 10 parts byweight of coumarone-indene resin, and approximately 0.4 part by weightof tetramethyl thiurammonosulphide, said vulcanized product being arelatively dense solid mass shaped to be useful for polishing said glassarticles.

7. An inherently substantially abrasive-free pad for use in polishingglass articles consisting of the vulcanized product of approximatelyparts by weight of butadiene-acrylonitrile copolymer rubber,approximately 50 parts by .weight of a blend of butadiene-acrylonitrilecopolymer and polyvinyl chloride, approximately 10 parts by weight ofsulphur,-approximately 6 parts by weight of zinc oxide, approximately 6parts by weight of benzothiazyl disulphide, approximately 4 parts byweight of zinc salt of coconut oil fatty acids, approximately 250 partsby weight of 'corn cob particles, approximately 50 parts by weight ofpolysulfide type synthetic rubber polymer, approximately 15 parts byweight of coumarone-indene resin, and approximately 0.4 part by weightof tetramethyl thiuram monosulphide, said vulcanized product being arelatively dense solid of controlled shape.

8. An inherently substantially abrasive-free pad for use in polishingglass articles, said pad comprising the vulcanized relatively densesolid product of Approximate Ingredient Parts By Weight bonding materialfrom the group consisting of natural 200 to 205.

rubber, butadiene-aerylonitrile copolymer rubber, or- 1 gamepolysulphlde rubber, blend of butadiene-aeryloptlltrilefcopolymer andpolyvinyl chloride, and mixtures ereo sulphur 4 to 12. Zinc oxide 5 to7. zinc salt of fatty acid 3 to 5. thiuram monosulphide 0.3 to 0.6benzothiazyl disulphid 4 to 6. plasticizer l 5 to 20. cellulosicparticles from the group consisting of corn cob 100 to 600.

and wood flours.

9. An inherently substantially abrasive-free pad for use in polishingglass articles, said pad comprising the vulcanized relatively densesolid product of hp roximate Ingredient P rts By Weight bonding materialfrom the group consisting of natural 200 to 205.

rubber, butadiene-acrylonitrile copolymer rubber, or-

game polysulphide rubber, blend of butadiene-acrylortitiltrilefcopolymerand polyvinyl chloride, and mixtures ereo and wood flours.

the polishing surface of said pad being formed with a plurality ofgrooves.

10. An inherently substantially abrasive-free pad for use in polishingglass articles, said pad comprising the vulcanized relatively densesolid product .of

the p lishing su f o ai p d b ng orme with a plurality of grooves.

Ingredient bonding material {mm the group consisting of natural rubber,.butadiene-acrylonitrile .copolymer rubber, organic poly sulphiderubber, blend olibutadiene acry- :lztlilnitrilecopolymerand-polywinylchlonde, andmlxtures ezeof.

plasticizer corucob particles,

'11. An inherently substantially abrasive-free pad for use in polishingglass articles, said 113d comprising the vulcanized relatively dense'solid product of EA Q QQ References Cited in the file .of this patentfgg g UNITED STATES PATENTS 494,472 Gardner Mar. 28, 1893 200101205.1,953,983 Benner s Apr. 10, 1934 2,318,578 .Bal zlet al. May 11, 19432,378,630 Hill June 19, 1945 2,384,684 Kistler Sept. 11, 1945 Ag -l2,388,568 Penning Nov. 6, 1945 2,8, 2,434,314 Felker Jan. 13, 19480.3150 0.6. 2,450,433 Leeman .Oct. 5, 1948 3:83 2,582,741 Ayers Jan. 15,1952 IOU/$0600. FOREIGN PATENTS 117,723 Australia Nov. 3, 1943 OTHERREFERENCES Ingredient bondingrnaterial from the group consisting ofnatural "rubber, butadiene-acrylonitrile lcopolymer rubber, organic,polysulphide rubber, .blend.ofbutadiene-agrylon'itrile copolymer andpolyvinyl chloride, .andmixtures thereof.

sulphur zinc oxide zinc salt of fatty acid thiurammonosulphidebenzothiazyl disulphide 'plaszicizen 1 corn cob particles Articledealing with Characteristics, Properties and Approximate Applications of.Geon ,Polyblend .by J. E. ,Pi'ttenger and lwi f G. F. Cohan, page 56315111 Rubber Age, August, 1947. mg Modern Plastics ,No. 32, vol. 25October 1947, pages 91 and 96. -200to 205.

41:0 12. 5-110 7. 3-t0 5. 0;3-t00.6. .4to 6.

8. AN INHERENTLY SUBSTANTIALLY ABRASIVE-FREE PAD FOR USE IN POLISHINGGLASS ARTICLES, SAID PAD COMPRISING THE VULCANIZED RELATIVELY DENSESOLID PRODUCT OF